What is needed to close the modelled global budget of ocean plastic debris?

Delphine Lobelle, Institute for Marine and Atmospheric Research Utrecht, Utrecht, Netherlands and Erik van Sebille, Utrecht University, Institute for Marine and Atmospheric research Utrecht, Utrecht, Netherlands
Plastic debris has become a ubiquitous issue in oceans around the globe. As well as numerous unknowns, such as the severity of this contemporary anthropogenically-caused threat to ecosystems and human health, plastic’s distribution in the oceans is still currently under investigation. With only around 1% of the total estimated global plastic entering the ocean being found at the surface, the focus of many groups is to improve the understanding of the remaining budget in order to eventually close the global inventory. Here, we present a framework, using the OceanParcels Lagrangian particle-tracking model to explore and compare some of the processes that are still poorly understood (such as biological growth on plastic over time, i.e., biofouling). Because of the limited number of direct observations, knowledge from previous case studies of other proxies (such as Sargassum seaweed) is applied. This framework can shed light on which processes are most important to the fate of plastic litter, and hence where previous estimations of plastic’s distribution throughout ocean basins can most effectively be improved.